In closed cycle refrigerating systems operating within usual household or commercial refrigeration temperature ranges, refrigerants utilized are typically Freon-type pure gases or, more recently, mixed gases, frequently utilizing Freon at least as one of the constituents. Such refrigeration systems operating in the household refrigeration range utilize equipment which can well reach within the desired pressure ratios, temperature ranges, and efficiencies required.
When operating cooling systems into the cryogenic range, refrigerants usually have boiling temperatures below 120.degree. K. such as nitrogen, argon helium, methane, and the like. These cryogenic gases have typically required the use of very high pressure gas systems involving multi-stage compressors or high pressure oil-less compressors. These systems therefore become more expensive to manufacture and operate, and require frequent maintenance.
In order to provide cryogenic systems which are less costly and more efficient, there have been proposed numerous mixed gas refrigerants for use within the cryogenic temperature range. In fact, many such mixed gas arrangements have been provided. These typically combine the standard well-known cryogenic refrigerants such as nitrogen, argon, neon, and the like, with various hydrocarbons, including methane, ethane, propane, and isobutane, in various combinations. Each of these have provided a specific arrangement of components with specified percentages of the various ingredients.
One reference that has heretofore described a mixed gas cryogenic refrigerant is Russian Pat. No. 627,154. This patent suggests a mixed gas refrigerant combining nitrogen with various ones of the hydrocarbons. One of the mixed gas refrigerants suggested includes the composition of nitrogen: 25-40% by molar weight, methane: 20-35% by molar weight, ethane: 15-35% by molar weight; and propane: 25-45% by molar weight.
Another reference which has suggested a combination of the same above ingredients, but in different proportions, is UK Pat. No. 1,336,892. There again, numerous types of combinations of the standard cryogenic refrigerants, such as nitrogen, are combined with various ones of the hydrocarbons have been suggested. In one of those combinations, they also teach the combination of nitrogen: 20-70% by molar weight (specifically recited as volume); methane: 10-30% by molar weight; ethane: 10-25% by molar weight; and propane: 10-25% by molar weight.
While each of these two references teach specific percent compositions of the same four ingredients, it has been found that the efficiencies and refrigeration per unit volume of gas entering the compressor, varies for each of these combinations. Furthermore, it has been found that through an understanding of specific temperatures and pressures required in a cryogenic system, it is possible to make a more specific selection of molar fraction percent of the ingredients in order to achieve an even greater and unexpectedly improved efficiency and value of refrigeration per unit volume of gas entering the compressor. Such unexpected results have been found by redefining the percent concentration of the various ingredients, wherein the unexpected improvement has resulted.